Do You Know These Illuminating Facts About LEDs?

The LED is a light emitting diode that is used in various display and lighting applications among others. Essentially it is a PN junction semiconductor diode that emits photons when it is forward biased. This light emitting effect of the LED is called injection electroluminescence.

Injection electroluminescence or the light emitting process in a LED occurs when minority carriers recombine with carriers of the opposite type in a diode's band gap. The wavelength of the emitted light varies primarily due to the choice of semiconductor materials used as the band gap energy varies with the semiconductor.

LEDs are processed in wafer form similar to silicon integrated circuits, and broken out into dice. Chip size for visible signal LEDs generally fall in the range 0.18mm square to 0.36mm square. InfraRed (IR) LEDs can be larger to handle peak powers, and LEDs for lighting are larger again.

The basic structure of an LED indicator - the simplest packaged LED product, consists of the die, a lead frame which houses the die, the encapsulation epoxy which protectively surrounds the die, and also disperses the light.

The dispersion or radiation pattern of the light is determined by the LED lamp’s mechanical construction.

Generally, LEDs have a mean time between failures in the range of 100,000 to over 1,000,000 hours. Considering a year is 8760 or 8784 hours, this is a very long period of time. In practice, LEDs are deemed to have reached the end of their life when the light output falls to half.

Typically, when current flow within a LED junction is not uniform, small temperature differentials occur within the chip. This exerts stress on the lattice, causing minute cracks to occur. In time, this accumulation of defects reduces the photon conversion efficiency of the chip, thus reducing light output. This rate is influence by various factors including LED material, temperature, humidity, and current flow.

Essentially two technologies for generating white light from LEDs exist. One is to mount a red die, a green die, and a blue die together within a package, and mix the light outputs in correct proportions to achieve white light. The usage of 3 dice in this approach makes it costly although tricolor LEDs are popular for LCD backlights in consumer applications.

The quantum efficiency of LEDs is ever increasing with availability of all primary colors (RGB) and reliability as good as the other display technologies. Surface mount LEDs are used in backlights for smaller LCD panels, equipment panels, and indoor message boards. Outdoor message boards are also LEDs for advertising displays and traffic signs. The durability and effectiveness of LEDs makes them ideal traffic lamp replacements for incandescent lamps.

Currently, most ultra brightness LEDs easily exceed the light output of incandescent and halogen lamps and do not need maintenance requirements of filament lamps. The challenge of LED process developers now is to build a very high brightness white LED which is economic enough to be used for domestic lighting. With the rapid advent in LED technology and innovation, anything is possible.